releases/2.6.36.2/kvm-vmx-fix-host-userspace-gsbase-corruption.patch

   1 From c8770e7ba63bb5dd8fe5f9d251275a8fa717fb78 Mon Sep 17 00:00:00 2001
   2 From: Avi Kivity <avi@redhat.com>
   3 Date: Thu, 11 Nov 2010 12:37:26 +0200
   4 Subject: KVM: VMX: Fix host userspace gsbase corruption
   5
   6 From: Avi Kivity <avi@redhat.com>
   7
   8 commit c8770e7ba63bb5dd8fe5f9d251275a8fa717fb78 upstream.
   9
  10 We now use load_gs_index() to load gs safely; unfortunately this also
  11 changes MSR_KERNEL_GS_BASE, which we managed separately.  This resulted
  12 in confusion and breakage running 32-bit host userspace on a 64-bit kernel.
  13
  14 Fix by
  15 - saving guest MSR_KERNEL_GS_BASE before we we reload the host's gs
  16 - doing the host save/load unconditionally, instead of only when in guest
  17   long mode
  18
  19 Things can be cleaned up further, but this is the minmal fix for now.
  20
  21 Signed-off-by: Avi Kivity <avi@redhat.com>
  22 Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
  23 Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
  24
  25 ---
  26  arch/x86/kvm/vmx.c |   15 +++++++--------
  27  1 file changed, 7 insertions(+), 8 deletions(-)
  28
  29 --- a/arch/x86/kvm/vmx.c
  30 +++ b/arch/x86/kvm/vmx.c
  31 @@ -828,10 +828,9 @@ static void vmx_save_host_state(struct k
  32  #endif
  33
  34  #ifdef CONFIG_X86_64
  35 -       if (is_long_mode(&vmx->vcpu)) {
  36 -               rdmsrl(MSR_KERNEL_GS_BASE, vmx->msr_host_kernel_gs_base);
  37 +       rdmsrl(MSR_KERNEL_GS_BASE, vmx->msr_host_kernel_gs_base);
  38 +       if (is_long_mode(&vmx->vcpu))
  39                 wrmsrl(MSR_KERNEL_GS_BASE, vmx->msr_guest_kernel_gs_base);
  40 -       }
  41  #endif
  42         for (i = 0; i < vmx->save_nmsrs; ++i)
  43                 kvm_set_shared_msr(vmx->guest_msrs[i].index,
  44 @@ -846,11 +845,14 @@ static void __vmx_load_host_state(struct
  45
  46         ++vmx->vcpu.stat.host_state_reload;
  47         vmx->host_state.loaded = 0;
  48 +#ifdef CONFIG_X86_64
  49 +       if (is_long_mode(&vmx->vcpu))
  50 +               rdmsrl(MSR_KERNEL_GS_BASE, vmx->msr_guest_kernel_gs_base);
  51 +#endif
  52         if (vmx->host_state.gs_ldt_reload_needed) {
  53                 kvm_load_ldt(vmx->host_state.ldt_sel);
  54  #ifdef CONFIG_X86_64
  55                 load_gs_index(vmx->host_state.gs_sel);
  56 -               wrmsrl(MSR_KERNEL_GS_BASE, current->thread.gs);
  57  #else
  58                 loadsegment(gs, vmx->host_state.gs_sel);
  59  #endif
  60 @@ -859,10 +861,7 @@ static void __vmx_load_host_state(struct
  61                 loadsegment(fs, vmx->host_state.fs_sel);
  62         reload_tss();
  63  #ifdef CONFIG_X86_64
  64 -       if (is_long_mode(&vmx->vcpu)) {
  65 -               rdmsrl(MSR_KERNEL_GS_BASE, vmx->msr_guest_kernel_gs_base);
  66 -               wrmsrl(MSR_KERNEL_GS_BASE, vmx->msr_host_kernel_gs_base);
  67 -       }
  68 +       wrmsrl(MSR_KERNEL_GS_BASE, vmx->msr_host_kernel_gs_base);
  69  #endif
  70         if (current_thread_info()->status & TS_USEDFPU)
  71                 clts();